OX500 mini scuba tank: a few minutes of air for the jobs under your boat

The OX500 is the simplest tank in the OXSEA range. Half a litre of air at 200 bar in an aluminium cylinder, a silicone mouthpiece and a pressure gauge built into the head. Nothing to strap on, no hoses, no BCD. You put it in your mouth, breathe as you normally would and go under for a look.

Most owners keep it in a hatch on the boat, next to the first aid kit, and forget about it until the day something goes wrong under the waterline.

The jobs it is made for

• A rope or a pot line round the prop. Crab pot floats in Queensland estuaries, cray pot lines off WA, South Australia and Tasmania, a mooring pick-up line sucked in when you back off. Cutting it free takes a few minutes with a knife and a tank. Our guide to freeing a rope from the propeller explains how.
• Checking the anodes. Between two antifouls, a look at the anodes on the leg, the shaft or the trim tabs tells you whether they will last the season. See how often to change boat anodes.
• An anchor that will not come up. Wedged under a rock ledge, or wrapped round something on the bottom. Before you cut the rode, a minute at the bottom usually sorts it.
• A blocked raw-water intake. Weed or a plastic bag over the intake makes the engine overheat. It clears from the outside in seconds.
• Getting comfortable. A first breath underwater is easiest in a backyard pool or in water you can stand up in.

How long it lasts

At 200 bar, half a litre of tank holds roughly 100 litres of air once it expands. A standard 12 litre dive cylinder filled to the same pressure holds about 2,400. That is the scale: the OX500 is a tool for a few minutes, not a dive.

Breathing calmly near the surface, you get up to 8 minutes. Working hard, cold water or a rush of adrenaline all make you breathe faster. Decide on a time to head up that sits well short of the maximum, and check the gauge.

Refilling

The tank arrives empty. You fill it before the first use and after each job, with one of two systems sold in the packs on oxsea.shop:

• The hand pump: about 20 minutes per fill, no power at all. Useful at a boat ramp, on a pontoon or at a campsite.
• The 12 V / 220 V compressor: about 12 minutes per fill, from the boat's house battery, a car battery or mains power.

Where it stops

• Two-handed jobs. You hold the OX500 with your mouth and usually a hand. Changing an anode or scraping a prop with both hands is easier with the OX500Plus, the same tank on a harness with the regulator on a hose.
• Dives. It does not replace scuba gear or scuba training. It is made for short stays at shallow depth, right by the boat.
• Fishing. Under Australian fishing rules a mini tank counts as underwater breathing apparatus, and several states ban taking fish with one. Read what each state allows before you take a speargun anywhere near it.

Before you jump in

Breathe continuously, never hold your breath on the way up and ascend slowly. Engine off and keys out before anyone goes near the prop. Put the Code Flag A up: other boats have to keep their distance, and the distance differs from state to state, as our dive flag guide shows. From K'gari north, across the Top End and down the WA coast to Exmouth, read our stinger season guide first, and in the north, our guide to crocodile country. The safety guide on oxsea.shop covers the rest.

OX500 or another tank?

If you mostly...	Look at
Check the prop, the anodes or the anchor, a few minutes at a time	OX500
Need both hands, or want to wear the tank on your back	OX500Plus
Run out of air before the job is finished	OX1000
Work under a big boat or snorkel the reef for 20 minutes or more	OX2000

All four are side by side on the comparison page.